Magnetic encoder

ABSTRACT

A magnetic encoder, which comprises a stainless steel sheet; and an under coat adhesive containing epoxy resin and organopolysiloxane, a top coat adhesive containing phenol resin, or phenol resin and epoxy resin, and a rubber magnet, as successively laid one upon another on the stainless steel sheet, has distinguished water resistance and saline water resistance, and thus can be effectively used particularly as a magnetic encoder in wheel speed sensors.

TECHNICAL FIELD

The present invention relates to a magnetic encoder, and moreparticularly to a magnetic encoder with improved water resistance,saline water resistance, etc.

BACKGROUND ART

Magnetic encoders using a rubber magnet are excellent for detection ofrevolution rate at a low speed and recently have been widely used inwheel speed sensors, etc. Wheel speed sensors are used in theneighborhood position of wheel, requiring good water resistance and asaline water resistance. The magnetic encoder using a rubber magnetcomprises a stainless steel sheet, a rubber magnet, and an adhesive forbonding these two. Water resistance tests show that peeling occurred atthe interface between the stainless steel sheet and the adhesive of themagnetic encoder, and the water resistance of the adhesive as well asthe rubber magnet itself is regarded as very important.

For the adhesive layer for the water resistance purpose, epoxy resin isusually used, but owing to poor adhesion to the stainless steel sheet,the epoxy resin is not used alone in case of the stainless steel sheet.In case of a single adhesive layer, a phenol resin-based adhesive, asilane-based adhesive, an epoxy resin/silane-based adhesive, or the likeis used. In case of two adhesive layers, the afore-mentioned phenolresin-based adhesive, a phenol resin/halogenated polymer-bases adhesive,a phenol resin/epoxy resin-based adhesive, or the like is used as anunder coat. However, even if these under coat adhesives are used incombination with various top coat adhesives, no statisfactory waterresistance can be obtained in severe circumstances such as saline waterspraying.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a magnetic encoder withdistinguished water resistance, saline water resistance, etc., whichcomprises a stainless steel sheet and a rubber magnet, both being bondedto each other through an epoxy resin-based adhesive.

The object of the present invention can be attained by a magneticencoder, which comprises a stainless steel sheet; and an under coatadhesive containing epoxy resin and organopolysiloxane, a top coatadhesive containing phenol resin, or phenol resin and epoxy resin, and arubber magnet as successively laid one upon another on the stainlesssteel sheet.

The stainless steel sheet for use in the present invention includesthose of SUS304, SUS301, SUS430, etc. For the magnetic encoder use, thesheet thickness is usually about 0.2 to about 2 mm.

At first, an under coat adhesive containing epoxy resin andorganopolysiloxane is applied to the stainless steel sheet. As the undercoat adhesive containing epoxy resin and organopolysiloxane, an adhesivecomprising epoxy resin, organopolysiloxane, which is a hydrolysiscondensate of organoalkoxysilane represented by the general formula,Xn—Si(OR)_(4-n) (where X is a functional group reactive with rubber orresin, R is a lower alkyl group and n is 1 or 2), colloidal silica, andamide- or imide-based epoxy resin curing agent, is preferably used.

The epoxy resin for use in the present invention includes, preferablythose obtained by reaction of bisphenol A, bisphenol F or novolak resinwith epichlorohydrin. Commercially available epoxy resin can be directlyused as such an epoxy resin. For example, Epikote 154 (a product ofJapan Epoxy Resin Co.), Epikote 157S70 (ditto), Epikote 180S65 (ditto),etc. can be used. Aquous emulsion-type epoxy resin can be also used. Forexample, Epi-Rez, 5003W55 (a product of Japan Epoxy Resin Co.), Epi-Rez6006W70 (ditto), etc. can be used.

The organopolysiloxane for use in the present invention includeshydrolysis condensates of at least one of organoalkoxysilanesrepresented by the general formula Xn—Si(OR)_(4-n), where X is afunctional group reactive with rubber or resin such as methyl, ethyl,3-aminopropyl, N-(2-aminoethyl)-3-aminopropyl, N-phenyl-3-aminopropyl,vinyl, 3-methacryloxypropyl, 3-glycidoxypropyl, 3-mercaptopropyl, etc.,and R is a lower alkyl group such as methyl, ethyl, etc. Theorganoalkoxysilane represented by such a general formula includes, forexample, vinyltrimethoxysilane, vinyltriethoxysilane,3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane,N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane,N-β-(aminoethyl)-γ-aminopropyltriethoxysilane,3-glycidoxypropyltrimethoxysilane,3-glycidoxypropylmethyldiethoxysilane, etc.

Hydrolysis condensation reaction of organoalkoxysilane is carried out byheating at about 40° to about 80° C. for about 3 to about 24 hours inthe presence of an acid catalyst such as formic acid, acetic acid, etc.while keeping at least an equivalent weight of water for hydrolysispresent. Such hydrolysis condensates are preferably copolymerizationoligomers of amino group-containing alkoxysilane and vinylgroup-containing alkoxysilane. The amino group-containing alkoxysilaneas one member of the copolymerization oligomers includes, for example,γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane,N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane,N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, etc. The vinylgroup-containing alkoxysilane as another counterpart member includes,for example, vinyltrimethoxysilane, vinyltriethoxysilane, etc.

In the oligomerization reaction, 100 parts by weight of aminogroup-containing alkoxysilane, 25 to 400 parts by weight, preferably 50to 150 parts by weight, of vinyl group-containing alkoxysilane, and 20to 150 parts by weight of water for hydrolysis are used. When more than400 parts by weight of vinyl group-containing alkoxysilane is used, thecompatibility with the top coat adhesive or rubber will be deterioratedand consequently the adhesive-ness will be lowered, whereas in case ofless than 25 parts by weight the water resistance will be lowered.

The oligomerization reaction is carried out by charging thesealkoxysilanes into a reactor provided with a distillation appratus and astirrer, followed by stirring at about 60° C. for about one hour, thenadding thereto about 1 to about 2 moles of an acid such as formic acidor acetic acid on the basis of one mole of the amino group-containingalkoxy-silane within one hour, while keeping the reactor temperature atabout 65° C., followed by further stirring for 1 to 5 hours to proceedwith the reaction and distill off alcohol formed by hydrolysis underreduced pressure at the same time, discontinuing the distillation whenthe distillate is turned into only water, and diluting the residue to asilane concentration of 30 to 80 wt. %, thereby obtaining the desiredcopolymerization oligomer. The copolymerization oligomer is soluble inan alcoholic organic solvent such as methanol, ethanol, etc.Commercially available copolymerization oligomers can be used as such.

Colloidal silica for use in the present invention has particle sizes ofnot more than 50 nm and is selected in view of the species of a solventto be used. For example, when the solvent is water, commerciallyavailable products Snowtex 20 (a product of Nissan Chemical Industries,Ltd.), Snowtex 30 (ditto), etc. are used. When the solvent is an organicsolvent, Snowtex MEK-ST (ditto; dispersion in methyl ethyl ketone),Snowtex MIBK-ST (ditto; dispersion in methyl isobutyl ketone), etc. areused. To improve the film strength, colloidal silica is used in thefollowing mixing proportion.

As an amide- or imide-based epoxy resin curing agent, dicyandiamide,methylimidazole, etc. are used.

The components of the under coat adhesive are used in such proportionsas 45 to 75 wt. %, preferably 55 to 65 wt. %, of epoxy resin; 10 to 40wt. %, preferably 25 to 35 wt. %, of hydrolysis condensate oforganopolysiloxane; 3 to 10 wt. %, preferably 5 to 8 wt. %, of colloidalsilica; and 0 to 5 wt. %, preferably 0.5 to 3 wt. %, of amide- orimide-based epoxy resin curing agent, upon blending. When the hydrolysiscondensate of organopolysiloxane is used in a proportion of less than 10wt. %, the adhe-siveness to stainless steel sheet will be deteriorated,whereas in a pro-portion of more than 40 wt. % no improvement effect onthe water resistance and saline water resistance will be obtained.

As a solvent for the under coat adhesive comprising the foregoingcomponents such epoxy resin and organopolysiloxane, water or an organicsolvent is usually used. Any organic solvent can be used, so far as itcan dissolve epoxy resin, and acetone, methyl ethyl ketone, etc. arepreferably used. The under coat adhesive is a solution having aconcentration of about 1 to about 30 wt. %.

The under coat adhesive comprising epoxy resin and organopolysiloxane isapplied to a stainless steel sheet to a film thickness of about 5 toabout 30 μm by dipping coating, spraying coating, brush coating, etc.,followed by drying at room temperature and further drying at about 50°to about 250° C. for about 5 to about 30 minutes.

A phenol resin-based top coat adhesive is applied as a vulcanizationadhesive to the under coat adhesive comprising epoxy resin andorganopolysiloxane laid on the stainless steel sheet. Commerciallyavailable phenol resin-based adhesives can be used as such, and include,for example, Thixon 715 (a product of Rohm & Haas Co.). Metaloc N31 (aproduct of Toyo Kagaku Kenkyusho K.K.), Chemlok TS1677-13 (a product ofRhodes Far East Co.) etc. An adhesive containing phenol resin and epoxyresin, for example, Metaloc XPH-27 (a product of Toyo Kagaku KenkyushoK.K.), a composition containing novolak type epoxy resin and novolaktype phenol resin derived from p-substituted phenol, disclosed inJP-A-4-13790, etc. can be used. The same application method, applicationtemperature, and application time as in the case of the under coatadhesive are also applied to the top coat adhesive to form a top coatadhesive layer having a film thickness of about 5 to about 30 μm.

An unvulcanized rubber magnet is bonded to the adhesive layer so formed,and subjected to press vulcanization molding at about 150° to about 200°C. for about 5 to about 60 minutes to form a rubber magnet layer havinga thickness of about 0.5 to about 2 mm. Any rubber can be used for therubber magnet, so far as it can be bonded to the top coat adhesive, andNBR, ethylene-methyl acrylate copolymerization rubber (AEM), etc. can bepreferably used. Above all, a rubber composition for magnetic encoder,which comprises ethylene-methyl acrylate copolymerization rubber as abase polymer, magnetic powder such as ferrite magnet powder, etc.(usually used about 450 to about 1,000 parts by weight on the basis of100 parts by weight of the base polymer) and an amine-based vulcanizingagent can give a rubber magnet with distinguished heat resistance, waterresistance and saline water resistance.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will be described below, referring to Examples.

Reference Example

40 parts by weight of γ-aminopropyltriethoxysilane and 20 parts byweight of water were charged into a three-necked flask provided with astirrer, a heating jacket and a dropping funnel, and pH was adjust to 4to 5 with acetic acid, followed by stirring for several minutes. Whilefurther continuing stirring, 40 parts by weight of vinyltriethoxysilanewas slowly dropwise added thereto through a dropping funnel. After thedropwise addition, heating and refluxing were carried out at about 60°C. for 5 hours, followed by cooling to room temperature to obtaincopolymerization oligomer. The thus obtained amino group/vinylgroup-containing oligomer (organopolysiloxane) was used as a componentin the following adhesives A and B.

Examples 1 to 5 and Comparative Examples 1 to 6

At first, an under coat adhesive was applied to an SUS430 stainlesssteel sheet, followed by air drying at room temperature and successivedrying at 200° C. for 10 minutes, and then a top coat adhesive wasapplied thereto, followed by air drying at room temperature andsuccessive drying at 150° C. for 10 minutes. An unvulcanized rubbermagnet was bonded thereto, followed by press vulcanization at about 150°to about 200° C. for about 5 to about 60 minutes to obtain a rawmaterial for the magnetic encoder. Parts by weight (Adhesive) Remark:Figures in parentheses shows parts by weight on solid basis A: DPPNovolak type epoxy resin 175(100) (Epi-Rez 5003W55, a product of JapanEpoxy Resin Co.; solid concentration: 57 wt. %) Amino group/vinylgroup-containing 115(42)  organopoly-siloxane (solid concentration: 36.5wt. % in aqueous solution) Colloidal silica (Snowtex 20, a product50(10) of Nissan Chemical Industries, Ltd.; solid concentration: 20 wt.% in aqueous dispersion) Dicyandiamide (epoxy resin curing agent) 4Water 1610 B: o-Cresol novolak type epoxy resin 100(100) (Epikote180S65, a product of Japan Epoxy Resin Co.) Amino group/vinylgroup-containing 280(42)  organosiloxane (Solid concentration: 15 wt. %in acetone solution) Colloidal silica (Snowtex MEK-ST; 33(10) a productof Nissan Chemical Industries, Ltd; solid concentration: 30 wt. % inmethyl ethyl ketone) Dicyandiamide (epoxy resin curing agent) 4 Methylethyl ketone 1535 C: Phenol resin-based (Thixon 715, a product of Rhom &Haas Co.) D Phenol resin-based (Metaloc N-31, a product of Toyo KagakuKenkyusho K.K.) E: Phenol resin-based (Chemlok TS1677, a product ofRhodes Far East Co.) F: Phenol resin/epoxy resin-based (Metaloc PH-20, aproduct of Toyo Kagaku Kenkyusho K.K.) G: Phenol resin/epoxy resin-based(Metaloc XPH-27, a product of Toyo Kagaku Kenkyusho K.K.) H: Phenolresin/halogenated polymer- based (Chemlok 205, a product of Lord FarEast Co.) The foregoing adhesives were all diluted to a solidconcentration of 8 wt. % with methyl ethyl ketone, before use.(Unvulcanized rubber magnet) NBR (N220S, a product of JSR) 90 Liquid NBR(Nipol 1312, a product 10 of Nippon Zeon Co,. Ltd.) Strontium ferritepowder (FH-801, 800 a product of Toda Kogyo K.K.) Zinc white 3Antioxidant (Nocrack CD, a product 2 Ouchi Shinko Kagaku K.K.) Stearicacid 2 Plasticizer (RS700, a product of 5 Asahi Denka Kogyo K.K.) Sulfur0.8 Cross-linking aid (Nokceller TT, 2 a product of Ouchi Shinko KagakuK.K.) Cross-linking aid (Nokceller CZ, 1 a product of Ouchi ShinkoKagaku K.K.)

The raw materials for the magnetic encoder obtained in the foregoingExamples and Comparative Examples were subjected to an initialadhesiveness test, a water resistance test, and a saline water energizedtest.

Initial adhesiveness test: To determine percent retained rubber (R) inthe initial state, according to JIS K-6256 90° peeling test procedure

Water resistance test: To determine percent retained rubber (R) afterdipping a peeling test piece in water at 80° C. for 70 hours or 140hours, according to JIS K-6256 90° peeling test procedure

Saline water energized test: To determine percent retained rubber (R)after applying a 2A steady-state current (maximum volt: 16V) to betweena JIS K-6256 90° peeling test piece at a − electrode and an aluminumplate at a + electrode in an aqueous 3 wt. % sodium chloride solution at30° C. for 5 hours or 10 hours, according to JIS Z-2371

Results of determination in the foregoing Examples 1 to 5 andComparative Examples 1 to 6 are shown in the following Table 1, togetherwith the species of the under coat adhesives and the top coat adhesives,and heating-drying conditions used therein. TABLE 1 Comparative ExampleNo. Example No. Test item 1 2 3 4 5 1 2 3 4 5 6 [Under coat adhesive]Species A A A A B A B C C F H [Top coat adhesive] Species C D E G C — —— C C C [Initial adhesiveness test] Initial (R; %) 100 100 100 100 100100 100 100 100 100 100 [Water resistance test] After 70 hrs (R; %) 100100 100 100 100 100 100 80 90 100 80 After 140 hrs (R; %) 100 100 100100 100 80 80 20 50 80 20 [Saline water energized test] After 5 hrs (R;%) 100 95 100 100 95 80 80 0 30 90 20 After 10 hrs (R; %) 95 90 95 95 9040 40 0 0 50 0

Examples 6 to 10 and Comparative Examples 7 to 12

In Examples 1 to 5 and Comparative Examples 1 to 6, an unvulcanizedrubber magnet having the following composition was used: Parts by weightAEM (Vamac G, a product of DuPont-Dow 100 Elastomer Co.) Strontiumferrite powder (FH-801, a product of 700 Toda Kogyo K.K.) Stearic acid 2Antioxidant (Nocrack CD, a product of 2 Ouchi Shinko Kagaku K.K.)Plasticizer (RS735, a product of Asahi Denka Kogyo 10 K.K.)Cross-linking aid (Nokceller DT, a product of 4 Ouchi Shinko KagakuK.K.) Cross-linking agent (Diac No. 1 a product of 2 DuPont-DowElastomer Co.)

Raw materials for the magnetic encoder obtained in the foregoingExamples 6 to 10 and Comparative Examples 7 to 12 were subjected to aninitial adhesiveness test, a water resistance test, and a saline waterenergized test. Results of determination are shown in the followingTable 2 together with the species of the under coat adhesives and thetop coat adhesives used therein. TABLE 2 Comparative Example No. ExampleNo. Test item 6 7 8 9 10 7 8 9 10 11 12 [Under coat adhesive] Species AA A A B A B C C F H [Top coat adhesive] Species C D E G C — — — C C C[Initial adhesiveness test] Initial (R; %) 100 100 100 100 100 100 100100 100 100 100 [Water resistance test] After 70 hrs (R; %) 100 100 100100 100 100 100 95 95 100 95 After 140 hrs (R; %) 100 100 100 100 100 9595 40 60 95 40 [Saline water energized test] After 5 hrs (R; %) 100 100100 100 100 100 100 20 30 100 30 After 10 hrs (R; %) 100 100 100 100 10070 70 0 0 70 0

INDUSTRIAL UTILITY

The present magnetic encoder has distinguished water resistance andsaline water resistance, and thus can be effectively used particularlyas a magnetic encoder for wheel speed sensors.

1. A magnetic encoder, which comprises a stainless steel sheet; and anunder coat adhesive containing epoxy resin and organopolysiloxane, a topcoat adhesive containing phenol resin, or phenol resin and epoxy resin,and a rubber magnetic as successively laid one upon another on thestainless steel sheet.
 2. A magnetic encoder according to claim 1,wherein the under coat adhesive comprises epoxy resin,organopolysiloxane as a hydrolysis condensate of organoalkoxysilanerepresented by the general formula Xn—Si(OR)_(4-n), where X is afunctional group reactive with rubber or resin, R is a lower alkylgroup, and n is 1 or 2, colloidal silica, and an amide- or imide-basedepoxy resin curing agent.
 3. A magnetic encoder according to claim 2,wherein the under coat adhesive composition comprises 45 to 75 wt. %epoxy resin, 10 to 40 wt. % of organopolysiloxane, 3 to 10 wt. % ofcolloidal silica, and 0 to 5 wt. % of an amide- or imide-based epoxyresin curing agent.
 4. A magnetic encoder according to claim 2, whereinthe organopolysiloxane is copolymerization oligomers of aminogroup-containing alkoxysilane and vinyl group-containing alkoxysilane.5. A magnetic encoder according to claim 1, wherein a base polymer ofthe rubber magnet is NBR or ethylene-methyl acrylate copolymerizationrubber.
 6. A magnetic encoder according to claim 1, for use in wheelspeed sensors.
 7. A magnetic encoder according to claim 3, wherein theorganopolysiloxane is copolymerization oligomers of aminogroup-containing alkoxysilane and vinyl group-containing alkoxysilane.8. A wheel speed sensor that comprises the magnetic encoder according toclaim 1.